Gross and Histological Features of a Myofascial Trigger Point in the Upper Trapezius

The purpose of this study was to precisely locate, in living humans, a myofascial trigger point associated with the upper portion of the trapezius muscle (TrP1) that refers pain to the head and neck and to determine if this point is associated with anatomical structures. This study is descriptive and utilizes data from measurements of the location of TrP1 in relation to anatomical landmarks, of pressure sensitivity overlying the trigger point and electromyography recordings in localizing the trigger point. Information obtained from living humans was used to determine anatomical correlation to structures in cadavers. Results indicated there is little variability in the location of TrP1 among individuals or from one extremity to the other, and this point may be associated with structures of the skin. A neurovascular supply (NAV) emerging from the upper trapezius to the skin was located in cadavers resembling the location of TrP1 in living humans. This NAV contained only small diameter nociceptive nerve fibers. Conclusion from the study show that TrP1 in living humans can be precisely located and that the mechanism of pain referral may involve structures of the skin. Future studies to precisely locate other myofascial trigger points may aid in identifying mechanisms of trigger point activation as well as aid clinicians in more precisely locating trigger points for treatment